Tashfeen Malik entered the U.S. last year after telling authorities she was coming to marry Syed Farook and clearing government background checks.

Last week, she pledged her allegiance to the Islamic State group and, armed with an assault-style rifle, carried out an attack with her husband on his co-workers that left 14 dead, authorities said.

Scattered details of her life, and signs of her possible motivation, are emerging:

WERE MALIK AND FAROOK RADICALIZED?

Investigators believe they were but are unsure how it happened or who, if anyone, helped shape their views.

"We don't know those answers," David Bowdich, assistant director of the FBI's Los Angeles office, said Monday.

Authorities said last week that the Pakistani-born Malik, 29, pledged her support for the Islamic State group and its leader under an alias Facebook account shortly before the assault in San Bernardino.

Malik and Farook later died in a gunbattle with police. Attorneys for Farook's mother and siblings have cautioned against a rush to judgment on their motivations.

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HOW DID THEY CRAFT A DEADLY PLAN IN SECRECY?

Malik and Farook, 28, were known as a quiet, religious couple with an infant daughter. Friends and family have said no one saw signs of any transformation into ruthless killers.

Even Farook's mother, who lived with them, was unaware of the plotting, according to the family attorneys.

Bowdich said agents have determined the couple practiced firing weapons within days of the shootings. Investigators found evidence of bomb-making materials at their home.

Malik's Facebook post has raised many questions, but Bowdich said agents don't know if Farook or Malik had a lead role.

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WHAT IS KNOWN ABOUT MALIK'S LIFE OUTSIDE THE U.S.?

According to officials, Malik lived in Pakistan from 2007 to 2014 before she headed to the U.S. on a fiancee visa.

Malik studied pharmacy at the Bahauddin Zakariya University in the central city of Multan, where she got a degree in 2013.

She also took classes at the Multan branch of Al-Huda International Seminary, a women-only madrassa, an Islamic religious school with branches across Pakistan and in the U.S. and Canada. The school has no known links to extremists, and in Pakistan it is popular among upper-middle-class and urban women.

The region where the school is located, however, is home to thousands of extremist seminaries, with hundreds linked to al-Qaida and the Pakistani Taliban.

Al-Huda said in a statement that it has no links to any "extremist regime" and seeks to promote a "peaceful message of Islam and denounce extremism, violence and acts of terrorism."

Pakistani authorities also have been looking into Malik's time in Multan. Pakistani police and intelligence agents have searched the house where she lived there, seizing documents, family photo albums and a laptop belonging to Malik's sister.

Former college classmates of Malik and others who knew her in Pakistan said that in recent years she began dressing more conservatively — including wearing a traditional Muslim scarf that covered nearly her entire face — and became more fervent in her faith. Former classmate Afsheen Butt said Malik showed drastic changes after a trip to Saudi Arabia in late 2008 or early 2009, and distributed Islamic religious literature.

The Farook family attorneys describe Malik as a reserved housewife who hewed to traditional behavior.

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HOW DID MALIK ENTER THE U.S. IN 2014?

Malik passed several government background checks and entered the U.S. in July 2014 on a K-1 visa, which allowed her to travel to the country and get married within 90 days of arrival.

The U.S. government has said there was vigorous vetting of her background, including in-person interviews, fingerprints, checks against terrorists watch lists and reviews of her family members, travel history and places where she lived and worked.

Foreigners applying from countries recognized as home to Islamic extremists, such as Pakistan, undergo additional scrutiny.

Following the marriage, the immigrant becomes a conditional resident for two years. After that waiting period, they must ask the U.S. government to remove the conditions and undergo another background check.